Throughout this application various publications are referred to in brackets. Full citations for these references may be found at the end of the specification immediately preceding the claims. The disclosures of these publications more fully describe the art to which the subject application pertains.
Nitric oxide (NO) is a small, diatomic gaseous molecule with numerous biological functions. Most notably, it is the major endothelial relaxing factor that relaxes smooth muscle by activating guanylate cyclase, which, downstream, results in vasodilation via a cyclic guanosine monophosphate-dependent pathway [1; 2; 3]. NO has many other functions that highlight its biomedical importance and therapeutic potential. NO inhibits platelet aggregation [1; 4], plays a major role in macrophage-mediated inflammatory response [1; 5; 6; 7], has antioxidant properties that prevent lipid peroxidation [8; 9], and can function as a signaling molecule in several tissue types including neurons and fibroblasts [1; 10]. The particular physiological consequence of NO is dependent not only on the site/compartment of production but also on both the rate and amount of NO generated at that location. Despite the many potential therapeutic benefits of supplemental NO, its use as a therapeutic has been limited. This limitation is due in part to the ongoing challenge of creating a practical and economically feasible delivery vehicle for this moderately reactive molecule that is capable of sustained delivery of the appropriate amount of NO to a desired target site [11].
Over the past few decades, several NO-related therapeutics have emerged, though are generally based on complex chemical systems. Unfortunately, these chemical reagents typically cannot spontaneously release NO. Instead, they rely on enzymatic activity to achieve release of NO [12]. These so-called pro-drugs include organonitrates, most notably nitroglycerine and organometallic NO-donors such as sodium nitroprusside. Disadvantages including progressive tachyphylaxis, resulting from depletion of host enzymes required for the generation of NO, potential toxicity from toxic byproducts (e.g., sodium nitroprusside decomposes releasing NO as well as cyanide) [13; 14; 15; 16; 17], and short lived biological impact, all limit their therapeutic efficacy. Gaseous NO, though effective and approved by the FDA for the treatment of pulmonary hypertension [18], is limited due to expense, requirement of delivery via gas tank, and potential toxicity issues from the production of NO2 [19]. Diazeniumdiolates (commonly referred to as NONOates) are a new class of chemicals which can release NO spontaneously. NONOates contain NO complexed with nucleophiles [20; 21; 22], allowing for controllable rates of NO release via various parameters including pH, temperature and the nature of the nucleophile with which the NO is complexed. Unfortunately, pulmonary and systemic toxicity induced by metabolites of NONOates are a potential issue, as is the formation of met hemoglobin (metHb) limiting red blood cell (RBC) oxygen carrying capacity [20].
Recently, novel hydrogel-based nanoparticle platforms have been described capable of releasing internally generated NO at biologically significant levels over sustained time periods [23; 24]. Upon IV infusion, these NO releasing nanoparticles (NO-nps) have been shown to induce long-lived vasodilatory effects in animal models in a dose-dependent manner with much greater efficacy and less metHb build up than NONOates [25]. These infused NO-nps have also been shown to be effective in reversing acellular Hb induced vasoconstriction and in limiting the inflammatory cascade in a hemorrhagic shock model [26]. Topical NO-nps have been effective in treating erectile dysfunction in rat models [27], have potent broad spectrum anti-microbial activity [28; 29] in vitro, and accelerate wound and abscess healing in murine models [30; 31; 32; 33].
S-nitrosothiols containing molecules (RSNOs) have come into the biotechnology spotlight recently as molecules that once formed, can extend both the temporal window and functionality for NO associated bioactivity in vivo [34; 35; 36; 37; 38; 39]. RSNO half-lives are measured in the minutes to hours [40; 41; 42], whereas free NO has been shown to have a half-life measured in the seconds or less depending on site of production [1]. RSNO-based therapeutics appear to have many very similar physiologic effects as other NO-related therapeutics [34; 43; 44; 45]. They are long-lasting bioactive vasodilators [13; 15; 19; 44] not subject to drug tolerance [13; 14; 15; 19; 46], relax smooth muscle [47], and prevent platelet aggregation [43]. In animal models NAC-SNO reduces plaque buildup secondary to hypercholesterolemia [48], acts as a hypotensive [15], an anti-inflammatory [49], and blocks lipid peroxidation that can limit non-alcoholic fatty liver disease pathology [8]. Much of the biological activity of RSNOs has been attributed to S-transnitrosation, where NO as a nitroso group is transferred from one thiol to another resulting in the nitrosation of reactive thiol containing proteins on cell surfaces, in cells, and in plasma.
The present invention addresses the need for a practical and economically feasible delivery vehicle that is capable of sustained delivery of NO to a desired target site.